Market available consumer batteries such as button cell batteries or zinc-carbon batteries are generally called primary cell. These batteries are designed to be used once and then discarded. As primary cells are used, chemical reactions in the battery use up the chemicals, thus generating power. When the chemicals are used up, the battery stops producing electricity. Primary cells are generally cheaper to manufacture, and tend to have lower retail prices. However, the heavy metals and electrolytes contained in primary cells are harmful to the environment, resulting in environmental pollution when they are discarded. For example, if electrolytes contained in the primary cells leak out, this may cause a chemical reaction with water, which then produces toxic substances.
In recent years, research for alternatives to traditional primary cells has made significant progress. A water-activated power generating device, generally known as a water battery, is an example of the alternatives. A water battery is a battery that does not contain any electrolytes, and hence produces no voltage until it is soaked in or filled with water. Therefore, in comparison with traditional primary cells, water batteries are easily stored, since chemical reactions will not occur if no water comes into contact with the water battery. Water batteries can be stored in warehouses or on shelves for years without consuming any of the chemicals in the water battery. Furthermore, the materials used for manufacturing water batteries are environmentally friendly, which means that when a water battery is discarded, the components of the water battery can be easily recycled, and do not produce toxic substances.
Water batteries can be made into various shapes and may have different sizes and dimensions. However, as modern portable electronic devices are designed to use standard primary batteries, it is common that water batteries are made in accordance with the primary battery standards. For example, water batteries made in accordance with the technical standards for battery sizes and types published by standards organizations such as International Electrotechnical Commission (IEC) and American National Standards Institute (ANSI) are available in the market in recent years.
Conventional water batteries have some drawbacks. As mentioned above, water batteries start to produce voltage/current until it is soaked in or filled with water. The water filling into a water battery sometimes leaks out and thus damages the electronic device that contains the water battery. In addition, the air/gas produced during the chemical reaction accumulates within the body of a battery, and if the water battery does not include a well-functioning air vent/channel for gas emission, the pressure in the body of the battery will increase and thus eventually damage the battery. The life of a water battery is another concern. The lifetime of a traditional water battery is sometimes shorter than a primary battery and thus adversely affects the market potential of water batteries.
Therefore, there is a need to develop a water-activated power generating device that overcomes the above-mentioned problems.